DE102010042351B4 - Microscope illumination system, microscope and oblique incident illumination method - Google Patents

Abstract

Microscope illumination system (1) with a light source (2, 3) and a diaphragm device with a diaphragm opening (9) for generating a central illumination beam path (15 ') centering on the optical axis (16), with a shifting of the diaphragm opening (9) in relation Illuminating beam path (15), which runs decentrally on the optical axis (16), can be generated for oblique incident light illumination, characterized in that the diaphragm device has a diaphragm disc (8) which can be rotated about an axis of rotation (11) and on which several diaphragm openings (9) of different diameters are circumferential Size are arranged, each of which can be positioned centered on the optical axis (16) or within a predetermined range around the optical axis (16) by rotating the diaphragm disk (8) to the optical axis (16).

Description

The present invention relates to a microscope illumination system according to the preamble of claim 1. Such a system comprises a light source and a diaphragm device with a diaphragm opening for generating a central illumination beam path centered on the optical axis, whereby a displacement of the diaphragm opening is decentered with respect to the optical axis Illumination beam path ("decentered illumination beam path") can be generated. In a microscope with reflected light illumination, such a microscope illumination system for object illumination with oblique reflected light can be used. Moreover, the invention relates to a corresponding method.

An investigation of objects in oblique reflected light is used, for example, in wafer inspection, in order to use the diffraction effects occurring on structures of the preparation surface to image these structures in a high-contrast and plastic manner. A usable for this purpose Auflichtilluminator for a microscope for illumination with oblique incident light with variable in size aperture stop is from the DE 35 27 426 C1 known. There, an aperture diaphragm device is presented, which has an aperture diaphragm which can be moved on both sides out of the optical axis. As the distance from the optical axis increases, the angle called the "incident light angle" increases, below which the axis of the illumination beam path, after passing through the microscope objective, falls onto the object plane (relative to the perpendicular to the object plane).

However, the proposed in the cited document construction of Auflichtilluminators proves to be mechanically complex and requires in practice training and experience of the user. In addition, the pivoting, as described in the Scriptures, depending on the arrangement in the tripod be limited. Finally, as also described in the document, the reproducibility of the direction of light incidence (corresponding to the pivotal movement of the aperture diaphragm device) is limited. The required rotation of the adjusting nut for varying the incident light angle makes a continuous change of the same during the microscopic examination almost impossible.

From the EP 0 069 263 B1 is a device for the selective realization of phase contrast and relief observation of microscopes known. For this purpose, a shutter is proposed, by means of which both object representations in the classical phase contrast as well as by the so-called modulation contrast method are possible by simply switching of apertures in the illumination beam path while maintaining the same lens. For pure phase contrast representation, a diaphragm with an annular transparent area in the shutter slide is proposed. To produce a relief effect, a further diaphragm is provided in the diaphragm slide, which has a light-permeable circular segment. This segment is rotatable so that the azimuth angle can be varied. In addition, the diaphragm shutter is followed by a ring which weakens the amplitude of the light transmitted through the circular segment.

From the DE 101 10 597 A1 an arrangement for attenuating an expanded light beam is known, which has a plurality of apertures, which are incorporated in a rotatably mounted disc. Here, the diameter and / or the density of the apertures in a direction of rotation of the disc varies. The expanded light beam thus hits depending on the position of the disc to more or fewer apertures or those with a smaller or larger cross-section. In this way, the light beam can be attenuated defined.

The DE 697 04 586 T2 deals with the provision of new types of diaphragms for changing the size and shape of the diaphragm surface. Apertures for off-axis illumination are proposed, which are arranged in particular on an aperture plate, wherein the corresponding apertures can be adjusted in a simple manner.

A technically simple and therefore cost-effective alternative to interference microscopy, which is advantageously used for phase objects, is reflected-light microscopy with oblique illumination, which is particularly suitable for observing surface reliefs. For this purpose, a Köhler epi-illumination is generally used, wherein oblique illumination on one side is provided by decentring the aperture diaphragm (see above DE 35 27 426 C1 ), while the all-round oblique illumination is realized by inserting central or annular apertures into the plane of the aperture stop.

Object of the present invention is to provide a microscope illumination system with which it should be possible in a technically simple, easy-to-use and reproducible way to realize an oblique incident illumination with variable aperture size and at the same time variable incident light angle. In addition, a corresponding microscope and a method for Auflichtmikroskopie be given at oblique illumination.

This object is achieved by a microscope illumination system with the features of claim 1. A corresponding microscope is Subject matter of claim 11, a corresponding method for incident light microscopy with oblique illumination is the subject of claim 21. Advantageous embodiments emerge from the respective subclaims and the following description.

According to the invention, the diaphragm device has an aperture disk rotatable about a rotation axis, on which a plurality of aperture openings of different sizes are arranged in the circumferential direction, each of which aperture can be positioned centered on the optical axis or within a predetermined range about the optical axis relative to the same by rotating the aperture disk is. The prerequisite for this is, of course, that the rotation axis of the diaphragm disc is outside the optical axis. Unless otherwise stated, it should be assumed without limiting the generality of a vertical illumination, in which the illumination beam path is guided over a beam splitter and the microscope objective on the object to be examined. The central illumination beam path leads here to an axial incident light bright field illumination, while a decentered illumination beam path leads to a one-sided oblique incident illumination, which is also referred to as "oblique illumination".

To clarify the terms used in this application "light incidence direction" and "Auflichtwinkel" reference is made to the known spherical coordinate system with its spherical coordinates. The incident light angle, that is to say the angle between the perpendicular on the object plane and the direction of incidence of the reflected-light illumination beam path, corresponds to the polar angle, while the light incident direction corresponds to the azimuth angle of the spherical coordinate system.

In a starting position, a certain aperture is centered to the optical axis of the microscope illumination system. Proceeding from this, by rotating the aperture disc about its axis of rotation in clockwise or counterclockwise direction, the aperture opening can be decentered with respect to the optical axis. Here, the incident light angle changes and - due to the circular path, which describes the aperture when adjusting the diaphragm disc - also the light incident direction. The latter, however, only to a small extent, since with small displacements of the optical axis, in particular at large distances of the optical axis of the rotation axis of the diaphragm disc, the circular path can be approximated by a straight line.

Due to the fact that the aperture disc has a plurality of apertures of different sizes, which are arranged on the disk in the circumferential direction, it is easily possible to change by positioning the aperture disk between the predetermined sizes of the apertures.

Due to the reproducible adjustability of a defined position of each aperture in a technically simple and easy-to-use manner, the invention makes possible an easily reproducible variation in particular of the incident-light angle on both sides of the optical axis while at the same time allowing the use of different aperture sizes.

The "predetermined area around the optical axis", within which a certain aperture can be positioned decentered to the optical axis, is principally characterized by the spacings of the apertures in the circumferential direction and on the other hand by the position of the respective aperture to the edge of the aperture disk, in FIG the practice but limited primarily by the diameter of the light source and illumination optics generated light beam bundle in front of the aperture. By arranging an aperture fixed diaphragm centered on the optical axis, in particular directly in front of the diaphragm disk, such an area can be firmly set around the optical axis. In this case, "arranged directly in front of the diaphragm disc" means that the aperture fixed diaphragm is arranged in the direction of the light source adjacent to the diaphragm disc, wherein no further optically active elements are to be present between the aperture diaphragm and the diaphragm disc.

For the smoothest possible rotation of the diaphragm disc, it is expedient to drive the diaphragm disc with a stepper motor. A drive by means of other motors, eg. As well as DC motors or magnetic drives, is also possible. To bring the engine with the diaphragm disc in operative position, the installation of a gear, belt drive, ring gear o. Ä. In question. With suitable control, the aperture plate can alternatively be mounted directly on the motor axis. Stepping motors with the smallest possible step size allow a nearly continuous rotation of the diaphragm disc. In particular, the use of a stepping motor makes it possible to reliably reproduce a specific setting of the oblique reflected-light illumination, in particular a reflected-light angle dependent on a specific object.

Advantageously, the axis of rotation of the diaphragm disc is arranged parallel to the optical axis in the microscope illumination system such that the connecting line 17 the piercing points of the axis of rotation and the optical axis through the diaphragm disc an angle of substantially 45 degrees with the horizontal. "Essentially" means an accuracy of about 10 degrees, so that said angle should be in a range of 35 degrees to 55 degrees. By "horizontal" is meant in practice the horizontal line through the optical axis of the illumination beam path.

If one places a Cartesian coordinate system on the diaphragm disc originating the coordinate system in the axis of rotation of the diaphragm disc, wherein the x-axis represents the horizontal and the y-axis is the vertical, can be achieved with the specified advantageous arrangement of the axis of rotation relative to the optical axis that at Rotation of the aperture disc, the selected aperture is moved on a circular arc within the aperture fixed stop (or more generally the predetermined range around the optical axis) at about 45 degrees to the x and y axis. Said circular arc can be well approximated by a straight line in the practical dimensions of Apertur fixed aperture. If such an illumination beam path is guided onto the object plane as reflected-light illumination beam path via a microscope objective according to the principles of Köhler illumination, oblique incident illumination can be realized with respect to the corresponding x'-y 'coordinate system in the object plane in which direction of light incidence (azimuth angle) is about 45 degrees and the incident light angle can be adjusted by moving the aperture away from the optical axis (by rotating the aperture disc about the axis of rotation).

In this way, structures on the sample in north-south direction (parallel to the x'-axis) and at the same time structures in the east-west direction (y'-axis) can be made well visible. This can z. As structures on wafers, microelectronic components, solar panels, etc., which are studied on finished components or during the manufacturing process. Namely, if an aperture, for example, only in the vertical direction relative to the optical axis displaceable, ie in north-south direction relative to said Cartesian coordinate system in the aperture disc, this results in a below-explained microscope incident illumination after Köhler a variation of the incident light angle in horizontal direction relative to the object plane (ie in east-west direction in the corresponding Cartesian coordinate system of the object plane). Although structures with a north-south orientation on the preparation can be displayed well with such variable oblique reflected-light illumination, in particular structures in the east-west direction, ie parallel to the adjustment direction, are not better visible when the incident-light angle is varied. On the other hand, with the proposed 45 ° oblique illumination, structures with north-south orientation as well as structures with east-west orientation are clearly visible. In particular, it is not necessary for better visualization of such structures to rotate the stage, for example by 45 degrees. Such turntables are costly and would also allow only poor reproducibility.

In a further embodiment of the invention, it may be useful to arrange the axis of rotation of the diaphragm disc in at least one direction displaceable perpendicular to the optical axis. For this purpose, for example, the above-mentioned stepping motor, which can rotate the diaphragm disc about the axis of rotation, be moved in the x-y coordinate system of the diaphragm disc, for example in the x and / or y direction. In this way, in addition to the oblique 45 ° illumination, an adjustment in north-south and / or east-west direction could take place.

In addition, it has proved particularly advantageous to increase the contrast and increase the resolution of the oblique reflected light illumination when illuminated in the ultraviolet spectral range ("Oblique UV"). Illumination with the short wavelengths of the UV spectrum leads, according to the laws of physics, to a higher resolution than illumination in the visible range. As a light source is particularly suitable an LED, the light with a wavelength of 365 nm (referred to as "i-line" in English) emits. The ultraviolet spectral range extends from 400 to about 185 nm. Already in the case of axial incident-light bright-field illumination, the UV illumination brings a higher resolution, in addition to the transition to oblique reflected-light illumination, a plastic representation of the object structures. With the Oblique UV illumination, components with a larger topography can be inspected with increased resolution. Fine scratches, for example on bare wafers or the degree of leaching of photoresist on semiconductor structures can hereby be made visible.

A UV lens specially designed for this Oblique UV illumination, in conjunction with a UV beam splitter and a UV-sensitive camera, allow the user to visualize and optimize the UV image captured by the camera, for example on the monitor of a PC , However, there are also UV lenses (eg from the applicant) which are able to image both classical methods such as bright field illumination, dark field incident light and DIC incident light and also the same methods in i-line illumination (ie in UV radiation). Spectral range at 365 nm). There are also beam splitters that are "UV-optimized" but are also suitable for the corresponding methods in visual light.

Another important aspect of the invention relates to a microscope illumination system with a light source and a diaphragm device for the production of a centered one and the other Alternatively, a decentered illumination beam path, in which the spectral regions of the illumination can be changed in a simple manner. Separate protection is reserved for this aspect. For the sake of clarity, however, this aspect will be described below as an advantageous embodiment of the above-discussed microscope illumination system. As light sources known microscope illumination systems are usually different lamp houses with different lamp types as a light source available. To hide certain spectral ranges filters are used. For example, switching from the visual spectrum to the ultraviolet spectrum has always been associated with the manual or motorized swinging of filters. Such a switching of the spectral range can be effected in a technically simple manner by the microscope illumination system having two light sources of different spectrum or different wavelength ranges. By simply switching between the light sources, the illumination spectrum can then be changed without the need to operate filters. The prerequisite for this is, of course, that the light sources and the beam paths generated by them be suitably coupled into the illumination beam path of the microscope illumination system. In a simple way, this can be realized by means of a dichromatic beam splitter, via which the two light sources can be coupled into the illumination beam path. Of course, this aspect can be extended to more than two light sources.

The light sources can be designed in particular as LEDs, which are in particular controllable in their performance. As a result, the various LEDs can be switched on alternately, so that an easy switching, for example, between the visual and the ultraviolet (or the ultraviolet wavelength range at least partially enclosing) spectrum is possible. The power control can also be designed such that certain portions of different spectra with a certain intensity can be coupled simultaneously into the illumination beam path.

To realize incident illumination according to Köhler's principle, the diaphragm disc can be arranged in a plane conjugate to the light source of the microscope illumination system. In this case, the light source is imaged in the aperture disk or the aperture fixed aperture arranged directly in front of it. At the same time, the diaphragm of the microscope illumination system is arranged in a plane conjugate to the entrance pupil of the microscope objective. In this way a uniform illumination of the object plane is achieved.

The invention also provides a microscope with a microscope illumination system having at least one light source, as described above, and with at least one microscope objective. In practice, there is usually an objective changer with several microscope objectives, one of which can be selected. Incidentally, the microscope has the usual components, such as tube optics, eyepiece and / or camera, which, unless stated otherwise, should be combined under the term imaging optics. In such a microscope incident light illumination can be realized in that the illumination beam path of the microscope illumination system via a beam splitter, which is preferably arranged between the microscope objective and the imaging optics, is coupled into the beam path of the microscope, so that the lens focuses the light tufts on the specimen. Starting from the object, it is imaged onto the camera via the imaging beam path through the objective, the beam splitter and a tube optic.

The use of a diaphragm disc with different diaphragm openings has the advantage that much smaller aperture diaphragm diameter can be realized than when using, for example, an iris diaphragm. While iris diaphragms can only be closed to a diameter of about 1 mm, smaller apertures are possible as an aperture in the aperture disc. For example, a 150 × / 0.90 lens has a pupil diameter of 2.4 mm. When the aperture diaphragm is mapped into the lens pupil by a factor of 2, the aperture aperture diameter of the objective only requires 2.4 mm / 2 = 1.2 mm for the full illumination aperture of this objective. If you want to dimming the illumination side of this lens, the aperture diameter must be significantly smaller than 1.2 mm, better less than 1 mm, which is not possible with conventional iris diaphragms. If, in addition, a decentered illumination beam path is to be produced according to the invention whose diameter lies entirely outside the optical axis, the diaphragm diameter must be less than or equal to 0.6 mm for said objective. Again, this would not be possible with conventional iris diaphragms.

In the case of the abovementioned microscope, it is advantageous if in the case of several objectives, in each case one microscope aperture is assigned to a diaphragm aperture on the diaphragm of the microscope illumination system or can be assigned. Depending on the microscope objective used, a specific aperture with the appropriate aperture diameter can be selected for incident illumination. This assignment can be made by the user be or factory, for example by appropriate control of the respective components, be set. In another embodiment, such a microscope has a plurality of microscope objectives. In this case, a diaphragm aperture of a certain size on the diaphragm plate of the microscope illumination system is associated or assignable to these microscope objectives. Alternatively, at least one of the microscope objectives are assigned or assignable to a plurality of apertures. The assignment is expediently designed such that when changing a lens, the associated aperture or one of the associated apertures is rotated by means of appropriate rotation of the diaphragm disc in the target position, ie on the optical axis.

The ability to disperse different sized apertures around the circumference of the aperture disc, conveniently in a sequence of increasing diameters, achieves the same effect as opening or closing an iris diaphragm in the aperture plane. However, the reproducibility of this method is much higher than with an iris diaphragm. Depending on the differences in the diameters of adjacent apertures, it is also conceivable to associate two or more apertures with a specific microscope objective. The size of the aperture determines the size of the illumination aperture, which is known to result in lower optical resolution but higher contrast as the value decreases. Large openings result in higher illumination apertures with higher resolution and less contrast.

To optimize the microscopically obtained image in terms of resolution and contrast, it is particularly useful to provide a control unit which is in operative connection with a drive unit for rotating the diaphragm of the microscope illumination system and optionally additionally with the at least one light source of the microscope illumination system. In this case, the control unit can be designed, for example, such that, depending on illumination in the UV range or in the visual range, the corresponding microscope objective and the diaphragm aperture assigned to it are respectively moved into their starting position or target position. For example, depending on the selected spectrum of the light source, the associated aperture can be positioned for a more or less decentered illumination beam path.

It is particularly advantageous if, in order to evaluate a camera image, the control unit is in operative connection with a camera which displays the microscopic object image in the form of a camera image. The camera image can be evaluated for resolution and / or contrast using methods described below. By varying one or more of the adjustable parameters (spectrum of the light source, intensity of illumination, diameter of the aperture, reflected light angle and direction of light incidence and type of microscope objective) by means of the control unit, the camera image can be optimized. The corresponding found parameters can be adjusted accordingly for later similar investigations, whereby high reproducibility is given.

By controlling the at least one light source, for example, the spectrum or the wavelength range of the illumination as well as the intensity of the illumination can be set defined. By controlling the drive unit of the diaphragm disc, for example, the diameter of the diaphragm opening, the incident light angle (distance of the diaphragm opening to the optical axis) and the direction of light incidence (position of the diaphragm opening relative to the optical axis at the same distance) can be set defined.

Various optimizations of the camera image are possible: Firstly, the respectively displayed camera image can be optimized by varying one or more of the mentioned adjustable parameters. On the other hand, a series of camera images can be recorded at different settings (variation of said parameters), from which an optimal camera image is selected automatically or by a user. The settings corresponding to the optimum camera image can be selected for further camera images on this or similar objects.

The process of optimizing the camera image with the associated setting of said parameters is preferably carried out automatically by means of an image analysis device which is part of the control unit. This self-optimization of the camera image is then similar to a control loop, in which the input variables represent the aforementioned adjustable parameters, while the resulting output variable one or more evaluation criteria for the camera image, so at least resolution and / or contrast, are.

Finally, with respect to the already described illumination in the ultraviolet ("UV") spectral range, it is advantageous if said control unit is designed to activate, automatically or on the basis of user input, a light source having a spectrum in the ultraviolet wavelength range in the illumination beam path and by means of the drive unit of the diaphragm a reproducibly adjusts a user-definable aperture (alternatively a fixed aperture) to a position with respect to the optical axis. Even that one after the other Setting multiple defined positions may be useful to select the best position.

The invention also relates to a method for oblique incident illumination of objects to be examined microscopically. Numerous aspects of this method have already been explained above in connection with the microscope illumination system or microscope according to the invention. In this respect, the disclosure therein expressly refers to the inventive method. In the method according to the invention for oblique incident light illumination of objects to be examined microscopically, an aperture disk rotatable about a rotation axis, on which a plurality of aperture openings of different sizes are arranged in the circumferential direction, is arranged with respect to the optical axis of a microscope illumination system such that each aperture opening is rotated by rotating the aperture disk into one Starting position centered on the optical axis and can be arranged by further rotation within a predetermined range about the optical axis decentered to the optical axis. With regard to the advantages of this method, reference is explicitly made to the above explanations in connection with the microscope illumination system or microscope according to the invention.

It is advantageous if a light source with a spectrum in the ultraviolet range is used as the light source of the microscope illumination system, wherein it is particularly advantageous if (at least) two light sources in the ultraviolet or in the visual range are used, which in each case via a dichromatic beam splitter in the beam path of the microscope illumination system are coupled. These embodiments have already been explained in detail above. A re-treatment of these embodiments should therefore be omitted to avoid redundancies. The same applies to the embodiment, according to which a drive motor is used to rotate the diaphragm disc whose shaft coincides with the axis of rotation of the diaphragm disc. By "coincidence" is meant a connection of the axis of rotation and the shaft or a one-piece design.

In a method according to the invention, in which the illumination beam path centered or decentered relative to the optical axis is directed to the object to be examined via a microscope objective, it is advantageous if, depending on the selected microscope objective, an associated aperture is centered in said starting position relative to the optical axis , In this case, the association aperture-microscope objective can be pre-programmed at the factory and, for example, be made via a control unit, or else the assignment can be defined by the user. As a result, the user has another way to set the starting position of the aperture plate from which the appropriate incident light angle can be set.

The method according to the invention can be used in particular for optimizing a camera image of a microscopically examined object. For this purpose, the camera image is evaluated at least in terms of resolution and / or contrast. This evaluation can be done either by means of known image processing methods or according to here proposed evaluation methods, which are explained below. By rotating the aperture disc within the predetermined range around the optical axis, in other words by changing the incident light angle, the plasticity of the representation can be optimized.

An additional or alternative possibility for optimizing the camera image is the choice of a suitable aperture and / or a suitable microscope objective. For example, for a given microscope objective starting from the aperture associated with this lens by selecting a smaller or larger aperture opening or fade. The small illumination aperture then results in lower resolution with higher contrast compared to the larger illumination aperture, while the larger illumination aperture results in increased resolution with lower contrast compared to the smaller illumination aperture. Depending on the desired object magnification, the appropriate microscope objective is selected. In addition, a change of lens may be necessary when transitioning from illumination with visual light to UV light.

Another alternative or additional possibility of camera image optimization is finally the choice of the light source of the microscope illumination system. As already stated above, the observation in the visual region of the spectrum can be sufficient and advantageous; however, switching to UV illumination is advantageous for higher resolutions.

Possible methods for optimizing the camera image have already been explained in detail above in connection with the microscope with control unit according to the invention. To avoid repetition, the statements there are also intended to support the method according to the invention with regard to possible camera image optimizations.

The optimization of the camera image is effected in particular by the fact that different changeable settings on the microscope and / or on the microscope illumination system, ie in particular the just discussed possibilities of changing the incident light angle, the aperture, the microscope objective and / or the light source, the associated camera images of a selected object area recorded and from these camera images each to a representative section an intensity profile is created. Such an intensity profile consists in particular of the gray values of an image line plotted over the corresponding image line, for example as the number of pixels. Depending on the type of object, a three-dimensional intensity profile can also be created. In a next step, evaluation criteria for the obtained intensity profiles are drawn up. Particularly expedient evaluation criteria represent the number and slope of the flanks of an intensity profile or the number of extreme values in an intensity profile. While the number of flanks provides information about the contrast of the viewed image section, the number of extreme values (maxima and minima of the intensity profile or resp the gray values) information about the resolution in the considered image section. Instead of the intensity profile, the first mathematical derivative of the same can also be used for the evaluation, in which flanks of the intensity profile can be recognized by extreme values and extreme values of the intensity profile by zeroing. The intensity profiles of the individual camera images can then be compared with regard to the evaluation criteria and from this the optimum intensity profile with the associated camera image can be determined. This determination is made on the basis of the respective task. This can be, for example, to generate a picture of the highest possible resolution or to produce an image with an optimal compromise of high resolution and high contrast.

Another way of optimizing the camera image is to generate different camera images with stored parameters for changeable settings on the microscope and / or on the microscope illumination system and to let the user select the optimal camera image. In this case, the judgment of the camera images would be done visually by the user. The stored parameters include reflected light angles, d. H. Rotation of the aperture disc at a given aperture, light incidence direction, d. H. Direction of rotation of the diaphragm, illumination aperture, d. H. in the working position aperture, illumination spectrum, d. H. active light source with predetermined spectral range, intensity of the light source and type of microscope objective.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically with reference to an embodiment in the drawing and will be described in detail below with reference to the drawing.

figure description

1 schematically shows a perspective view of the basic structure of an embodiment of the invention Mikrospopbleuchtungssystems with associated microscope;

2 schematically shows a further embodiment of the structure 1 in a side view with a second light source and a control unit for optimizing the camera image;

3 shows an embodiment of an aperture disc of a microscope illumination system in three different rotational positions;

4 shows a microscopic image of an object area and the intensity profile of a selected image section in an object illumination with axial (central) reflected light;

5 shows the same representation as 4 with oblique unilateral reflected light illumination from a first direction of light incidence and

6 shows the same representation as the 4 and 5 in a one-sided oblique incident light from the zu 5 opposite light direction of incidence.

1 shows a microscope illumination system 1 in a schematic perspective view. The microscope illumination system 1 includes a light source 2 and two of the light source 2 downstream lenses 5 and 6 on the optical axis 16 of the microscope illumination system 1 are arranged. The light source 2 is from the lenses 5 and 6 , which can also be referred to as illumination optics, imaged in the aperture plane, in which an aperture fixed aperture 12 is arranged. In the immediately underlying plane is the aperture disc 8th arranged. It contains circumferentially arranged apertures 9 , The aperture disc 8th is about a rotation axis 11 rotatable, which in this case with the shaft 11 ' a stepper motor 10 coincides. Instead of the stepper motor solutions with other drives, z. As a DC motor, or a magnetic drive conceivable. The Mechanical coupling can alternatively via gear, gears, timing belt, etc. take place. How out 1 seen, has a rotation of the aperture disc 8th around the axis of rotation 11 result in the apertures 9 through the aperture of the aperture 12 hike given area. In this way, out of the illumination beam path 15 ' in front of the aperture fixed aperture 12 a lighting beam path 15 after the aperture 9 generated by blanking.

Also on the optical axis 16 of the microscope illumination system 1 arranged are the lenses 13 and 14 taking the illumination beam path 15 continue in the direction of the beam splitter 20 conduct. The beam splitter 20 belongs to the microscope illumination system 1 and there has the function of redirecting the illumination beam path 15 on the object 36 in an object plane; on the other hand, the beam splitter 20 Part of the microscope 30 where he is part of the object 36 next imaging beam path (not shown) in the direction of the imaging optics 33 pass through.

In 1 shown very schematically is a microscope 30 that lens the essential ingredients 31 and imaging optics 33 having. The imaging optics 33 includes common components, such as tube optics, eyepiece and / or camera. Since it does not depend on these components in detail here, reference can be made to the prior art with regard to the structure and function of these microscope components. The microscope 30 further comprises an x'-y'-microscope stage 35 on which an object 36 stored in an object plane which is to be examined microscopically. In the present exemplary embodiment, this is a wafer which is to be examined, for example, for scratches or faulty structures. In a known manner, a microscopic image of the subject area under consideration is removed from the object 36 by lens 31 and imaging optics 33 generated. This microscopic image can either be visually perceived by a user by means of an eyepiece or taken by a camera and displayed on a monitor (not shown). Regarding the latter possibility, reference is made to the embodiment 2 directed.

In the following, the operation of the structure according to 1 described: Visually, it is in the in 1 illustrated Lukenstrahlengang to the realization of Köhler incident light illumination with vertical illumination (coupling of the illumination beam path via the lens of the microscope on the object plane). This is the aperture disc 8th in one to the light source 2 arranged conjugate level. At the same time is the aperture disc 8th in one of the entrance pupil of the microscope objective 31 arranged conjugate level. In this way, a uniform illumination of the object plane and thus of the observed preparation section is achieved. The light source 2 will be over from the lenses 5 and 6 existing illumination optics imaged in the aperture diaphragm plane. An aperture fixed aperture 12 centered to the optical axis 16 is arranged, specifies the maximum diameter of the aperture diaphragm. By means of a within the predetermined range of the aperture fixed aperture 12 located aperture 9 becomes out of the illumination beam path 15 ' a centered or decentered illumination beam path 15 generated. For a central bright field illumination (also called axial incident light bright field illumination) is in each case one of the apertures 9 the aperture disc 8th exactly on the optical axis 16 positioned. The size of the aperture 9 determines the size of the illumination aperture. In the transition from central to slant incident illumination, the aperture is 9 from its centered to the optical axis 16 moved outlying starting position. This movement takes place in the illustrated embodiment by rotating the aperture disc 8th around its axis of rotation 11 , which at the same time the axis or shaft 11 ' of the stepper motor 10 is. Depending on the direction of rotation of the stepper motor 10 wanders the aperture 9 obliquely upwards or downwards and is positioned at the desired target position.

Out 1 it can be seen that the axis of rotation 11 the aperture disc 8th parallel to the optical axis 16 of the microscope illumination system 1 runs and to this optical axis 16 "Is offset by 45 degrees". In exact terms, this means that the connecting line 17 the puncture points of the optical axis 16 through the aperture plate 8th and the axis of rotation 11 through the aperture plate 8th to the horizontal of the illumination beam path and thus to the x-axis of the drawn coordinate system includes an angle of 45 degrees (see. 3 ). The angle of 45 degrees is also included in the drawn y-axis. Of course, this 45 degree angle need not be an exact 45 degree angle. Deviations are possible and can even depending on the structure to be imaged on the object 36 be desired. Because the object 36 but usually on the microscope stage 35 arranged so that on the object 36 located structures in x'- and / or y'-direction, an offset by about 45 degrees arrangement is advantageous. In this way, one obtains namely a direction of light incidence which, relative to the coordinate system in the object plane with respect to the two axes x 'and y' also occupies an angle of 45 degrees. In this way, both in the x'-direction (NS-direction) and in the y'-direction (OW-direction) running structures are equally plastically represented.

A rotation of the aperture disc 8th causes the aperture 9 within the aperture fixed by the aperture 12 predefined area wanders on a circular arc whose radius is the distance of the optical axis 16 from the axis of rotation 11 equivalent. Further explanations can be found in connection with 3 , This movement of the aperture 9 As a result, with increasing distance from the optical axis 16 the incident light angle at the object 36 is enlarged. The light incidence direction remains approximately at an azimuth angle of 45 degrees, since in a good approximation said arc can be approximated by a straight line. This straight line runs at an angle of 45 degrees to the horizontal and thus to the x-axis.

In a further embodiment, the aperture disc 8th as a whole in the aperture diaphragm plane. For this example, the stepper motor 10 in turn movably mounted in the XY plane. A movement of the stepper motor 10 in the Y direction causes a shift of the illumination beam path 15 in the y'-direction in the object plane. Conversely, a movement of the stepping motor causes 10 in the X direction, a shift of the illumination beam path 15 in x'-direction in the object plane.

By using a light source 2 with emission in the UV spectrum (for example an LED with radiation of the so-called "i-line" of 365 nm), a higher resolution can be achieved than with illumination in the visual range because of the low wavelength. At the same time can by the described generation of a decentered illumination beam path 15 ' a plastic representation of structures on the object 36 be generated. This allows, for example, the representation of fine scratches on bare wafers or the visualization of the degree of leaching of photoresist on semiconductor structures. The oblique reflected light illumination with UV light is also called "oblique UV".

2 describes an arrangement that can be easily switched between two light sources. Further describes 2 an arrangement for optimizing a camera image, which is the microscopic imaging of structures on an object 36 contains. 2 shows as a basis essentially the same elements as 1 , which are provided with the same reference numerals. On a renewed discussion of 1 already known elements can therefore be dispensed with here. Only the additional elements are discussed below.

In addition to the light source 2 contains the microscope illumination system 1 another light source 3 that over lens 7 and a dichromatic plate 4 in the illumination beam path 15 ' is coupled. The other lens 6 is opposite 1 unchanged. Thus, the lenses form 5 and 6 for the light source 2 and the lenses 7 and 6 for the light source 3 the respective illumination optics. Furthermore shown in 2 Elements of the 1 known imaging optics 33 of the microscope 30 , These are the tube optics 32 and one behind the tube optics 32 switched camera 34 , The camera 34 takes the microscopic image electronically. On the one hand, the camera image can be displayed visually, on the other hand, it can also be processed electronically and evaluated with methods of image processing. The illustrated construction of a microscope 30 with lens 31 , Tube optics 32 and camera 34 is known per se to the person skilled in the art.

In 2 is still a control unit 40 shown. By means of this control unit 40 can be done fully automatic, but also semi-automatic optimization of the resulting camera image. For this purpose, an example will be described by way of example, without limiting the described in the general description part of this application variety of possibilities.

The control unit 40 is how out 2 visible, with the two light sources 2 and 3 , with the stepper motor 10 as well as with the camera 34 connected. The control of other components, in particular a (not shown here) objective turret on multiple lenses for selecting a suitable lens 31 , may be appropriate. The control unit 40 is with the light sources 2 and 3 connected in such a way that at least one alternate operation of these light sources, that is a turn on and off derselbigen is possible. In a further embodiment, the light sources 2 and 3 via the control unit 40 also controllable in their intensity or performance. The control unit 40 is with the stepper motor 10 connected in such a way that a certain on the aperture disc 8th located aperture 9 by turning the aperture disc 8th can be brought into a starting position in which the aperture 9 centered to the optical axis 16 of the microscope illumination system 1 is arranged. Subsequently, via the control unit 40 the stepper motor 10 be controlled to make a fine adjustment, in which the aperture 9 is moved out of its initial position to within the aperture fixed by the aperture 12 predetermined range to be moved to a defined target position (as in connection with 1 explained in detail). Finally, the control unit 40 with the camera 34 connected such that in the control unit 40 the camera image can be evaluated. This evaluation includes at least the criteria of resolution and / or contrast. Of course, the control unit 40 synonymous certain settings for image capture on the camera 34 make.

It is assumed that the light source 3 in the ultraviolet spectral range, the light source 2 emitted in the visual spectral range. The use of light-emitting diodes as light sources is advantageous 2 and 3 , The control unit 40 can the light sources 2 and 3 independently of each other, ie switching on and off (and possibly regulating their performance). By choosing the appropriate light source, the desired resolution in the microscopic camera image can be taken into account, depending on the fineness of the structures on the object 36 depends which is to be examined. The switching between the light sources is possible in a simple manner without interposing and operating filters. The iris disk may have six or, in another embodiment, fourteen (or any other number) different apertures 9 contain. The apertures 9 have different sized diameters and are advantageously positioned in ascending order of diameter circumferentially on the disc. In practice, using a microscope 30 worked with a nosepiece so that different lenses 31 in the imaging beam path of the microscope 30 can be introduced. The choice of the lens depends on the desired magnification as well as other parameters, on the one hand of the structures on the object 36 , on the other hand depend on the light source used. In a UV illumination is advantageously a UV-compatible lens 31 used. A specific lens 31 can have one or more apertures 9 be assigned. A change of the apertures then has the same effect as the opening or closing of an iris diaphragm in the aperture plane. However, as already stated elsewhere, the reproducibility of this method is much higher than with an iris diaphragm, moreover, smaller diaphragm diameters can be achieved than with an iris diaphragm. Without limitation of generality, it is assumed below that each lens 31 exactly one aperture 9 on the aperture disc 8th assigned. This assignment is expediently in the control unit 40 program-technically filed so that automatically with a lens change the associated aperture 9 in their initial position centered on the optical axis 16 of the microscope illumination system 1 is driven. This is the aperture disc 8th by means of the stepper motor 10 around the axis of rotation 11 accordingly twisted. Thus, for example, it will be from a light source 2 . 3 to another light source 3 . 2 switched over, so can via the control unit 40 the corresponding lens 31 by turning the nosepiece on the optical axis 37 the imaging beam path of the microscope 30 are introduced and at the same time the associated aperture 9 by controlling the stepper motor 10 be returned to their original position.

It can now be a camera image of the microscopically imaged structures to be examined on the object 36 be generated. For example, an image with axial reflected illumination is first realized with selected parameters (light source, aperture, objective). Such a picture is for example in the in 4 shown. One recognizes there in the east-west direction repetitive structures that extend in a north-south direction. This is the recording of parallel structures of a wafer. Turn the selected aperture 9 in one direction within the aperture fixed aperture 12 given area around the optical axis 16 the incident light angle can be changed with an oblique unilateral 45 ° illumination. An image of the same object area created at a certain incident light angle (as in 4 ) shows 5 , 6 shows a similar recording, in which case the aperture disc was rotated by the same rotation angle in the opposite direction, ie at opposite incident light angle compared to 5 , The differences in the camera images are already clearly visible visually. In this way, a number of camera images can be recorded while varying the reflected light angle and the light incidence direction, and the optimum camera image can be determined. As a rule, the settings associated with the optimal camera image will depend heavily on the structure being imaged.

In addition to a variation of the incident light angle and the direction of light incident, of course, other parameters, such as the type of lens 31 , Aperture 9 and light source 2 . 3 , be varied.

An automatic optimization of the camera image can be done in an advantageous manner that, as in the 4 to 6 shown, to a given section 51 from the camera image 50 an intensity profile 52 is created, which in the 4 to 6 each centrally in the camera image 50 is displayed. The intensity profile 52 in this case forms the over the neckline 51 (Pixel distance) existing gray values. The transitions from a light to a dark gray scale range are marked by steep edges. Steep flanks stand for a high contrast. At the same time, the number of extreme values, maxima and minima, is in an intensity profile 52 for the resolution in the considered section 51 , In 4 The presence of many extremes indicates a high resolution, which in turn comes at the cost of image contrast. A comparison with 5 shows significantly less extreme values and thus a lower resolution, with a few steep flanks, which indicates a high contrast. The situation is similar 6 , While at 5 the deviations from a mean gray value (about 130 on the scale) are relatively high in both directions, are in 6 the deviations from the average gray value (about 120) to the top are only slight and only higher. This in turn indicates that the light-dark contrast in 5 is higher than in 6 ,

The evaluation of the intensity profiles discussed here 52 to a series of recorded camera images 50 can in a control unit 40 automated. In this way, those adjustable parameters which lead to a camera image optimized for example with respect to the contrast can be determined. After setting these parameters, the entire sample or a series of similar samples can be examined.

3 shows a plan view of a schematically illustrated aperture plate 8th with a total of six apertures 9 , The rotation axis is back with 11 designated. 3b shows a position of the aperture disc 8th as used for centered illumination (or axial incident illumination) while the 3a and 3c Represent positions that are used for an oblique incident illumination. The camera picture 50 according to 4 For example, with a position of the aperture disc 8th according to 3b be generated while the camera images 50 according to 5 and 6 can be generated with aperture disk positions, as in 3c respectively. 3a are shown.

The aperture fixed aperture is with 12 designated. It cuts out a predetermined area within which an adjustment of a selected aperture 9 can be done to vary the incident light angle. An adjustment beyond this given range leads to a total shading. Only with further rotation reaches the next available in the circumferential direction aperture 9 in through the aperture fixed aperture 12 predetermined area.

The optical axis of the microscope illumination system 1 is in turn with 16 designated. From the representation of 3 clearly shows that the connecting line 17 between optical axis 16 and rotation axis 11 in the drawing plane of 3 includes a 45 ° angle with the x axis. The circular arc, along which an adjustment of the aperture 9 when turning the aperture disc 8th is done, is shown in dashed lines. Along this dashed line must the remaining apertures 9 be arranged. At a fine rotation of the aperture disc 8th shifts the selected aperture 9 from its initial position at an angle of likewise approximately 45 ° to the x-axis, as far as this movement on the dashed circular path is approximated by a movement on a corresponding straight line.

LIST OF REFERENCE NUMBERS

1

Microscope illumination system

2

light source

3

light source

4

dichromatic divider

5

lens

6

lens

7

lens

8th

aperture disc

9

aperture

10

Drive unit, drive motor, stepper motor

11

axis of rotation

11 '

wave

12

Aperture fixed aperture

13

lens

14

lens

15, 15 '

Illumination beam path

16

optical axis

17

connecting line

20

beamsplitter

30

microscope

31

lens

32

tube optical system

33

imaging optics

34

camera

35

microscope stage

36

object

37

optical axis

40

control unit

50

camera image

51

neckline

52

intensity profile

Claims (32)

Microscope illumination system ( 1 ) with a light source ( 2 . 3 ) and a diaphragm device with an aperture ( 9 ) for generating an optical axis ( 16 ) centered central illumination beam path ( 15 ' ), whereby by moving the aperture ( 9 ) with respect to the optical axis ( 16 ) decentered illumination beam path ( 15 ) can be generated for an oblique incident light illumination, characterized in that the diaphragm device has a rotation axis ( 11 ) rotatable diaphragm disc ( 8th ), on the circumferentially a plurality of apertures ( 9 ) are arranged of different sizes, each of which by rotating the diaphragm disc ( 8th ) centered on the optical axis ( 16 ) or within a predetermined range around the optical axis ( 16 ) decentered to the optical axis ( 16 ) is positionable. Microscope illumination system according to claim 1, characterized in that the axis of rotation ( 11 ) of the diaphragm disc ( 8th ) parallel to the optical axis ( 16 ) is arranged such that the Connecting line of piercing points of the axis of rotation ( 11 ) and the optical axis ( 16 ) through the aperture disc ( 8th ) an angle of substantially 45 Degree with the horizontal (x) includes. Microscope illumination system according to claim 1 or 2, characterized in that for rotating the diaphragm disc ( 8th ) this a drive motor ( 10 ) is assigned in operative position. Microscope illumination system according to one of claims 1 to 3, characterized in that the axis of rotation ( 11 ) of the diaphragm disc ( 8th ) in at least one direction perpendicular to the optical axis ( 16 ) is arranged displaceably. Microscope illumination system according to one of claims 1 to 4, characterized in that in front of or behind the diaphragm disc ( 8th ) one to the optical axis ( 16 ) centered Apertur fixed aperture ( 12 ) is arranged. Microscope illumination system according to one of claims 1 to 5, characterized in that the light source ( 3 ) has a spectrum in the ultraviolet wavelength range. Microscope illumination system according to one of claims 1 to 6, characterized in that the microscope illumination system comprises two light sources ( 2 . 3 ) in different wavelength ranges, one of which at least partially encloses the ultraviolet wavelength range. Microscope illumination system according to claim 7, characterized in that in each case one of the two or both light sources ( 2 . 3 ) via a dichroic beam splitter ( 4 ) in the illumination beam path ( 15 ' ) is einkoppelbar or are. Microscope illumination system according to claim 7 or 8, characterized in that the light sources ( 2 . 3 ) are designed as LEDs. Microscope illumination system according to one of the preceding claims, characterized in that the diaphragm disc ( 8th ) in one to the light source ( 2 . 3 ) of the microscope illumination system ( 1 ) conjugate level is arranged. Microscope ( 30 ) with at least one light source ( 2 . 3 ) microscope illumination system ( 1 ) according to one of claims 1 to 10 and with at least one microscope objective ( 31 ). Microscope according to claim 11, characterized in that the diaphragm disc ( 8th ) of the microscope illumination system ( 1 ) in a to the entrance pupil of the microscope objective ( 31 ) conjugate level is arranged. Microscope according to Claim 11 or 12, in which a microscope objective ( 31 ) an aperture ( 9 ) of a certain size on the diaphragm ( 8th ) of the microscope illumination system ( 1 ) is assigned or can be assigned. Microscope according to claim 13, comprising a plurality of microscope objectives ( 31 ) and in which a plurality of microscope objectives ( 31 ) an aperture ( 9 ) of a certain size on the diaphragm ( 8th ) of the microscope illumination system ( 1 ) or is assigned to the at least one of the microscope objectives ( 31 ) several apertures ( 9 ) are assigned or can be assigned. Microscope according to one of claims 11 to 14, characterized in that a control unit ( 40 ) provided with a drive unit ( 10 ) for rotating the diaphragm disc ( 8th ) of the microscope illumination system ( 1 ) and / or with the at least one light source ( 2 . 3 ) of the microscope illumination system ( 1 ) is in operative connection. Microscope according to claim 15 with a camera ( 34 ) for displaying a microscopic object image in the form of a camera image, wherein the control unit ( 40 ) for evaluating the camera image with the camera ( 34 ) is in operative connection. Microscope according to claims 15 and 16, characterized in that the control unit ( 40 ) is configured such that by controlling the at least one light source ( 2 . 3 ) and / or the drive unit ( 10 ) of the diaphragm disc ( 8th ) of the microscope illumination system ( 1 ), with which a selected aperture ( 9 ) in the illumination beam path ( 15 ' ) and at defined positions with respect to the optical axis ( 16 ) is reproducibly adjustable, the camera image is optimized in terms of at least resolution and / or contrast. Microscope according to claim 17, characterized in that the control unit ( 40 ) is configured such that the optimization of the camera image with respect to at least resolution and / or contrast due to a selection of camera images and / or input of criteria by the user. Microscope according to claim 17, characterized in that the control unit ( 40 ) is configured such that the optimization of the camera image with respect to at least resolution and / or contrast is done automatically by means of an image analysis device. Microscope according to one of claims 16 to 19, characterized in that the control unit ( 40 ) is configured such that it automatically or due to a user input a Light source ( 3 ) with a spectrum in the ultraviolet wavelength range in the illumination beam path ( 15 ' ) and activated by means of the drive unit ( 10 ) of the diaphragm disc ( 8th ) a user-definable aperture ( 9 ) to one or more defined positions with respect to the optical axis ( 16 ) sets reproducibly. Method for oblique reflected-light illumination of objects to be examined microscopically ( 36 ), in which by moving one in the beam path of a microscope illumination system ( 1 ) arranged aperture ( 9 ) from one to the optical axis ( 16 ) of the microscope illumination system ( 1 centered position with respect to the optical axis (FIG. 16 ) decentered illumination beam path ( 15 ) is generated for the oblique Auflichtbeleuchtung, characterized in that the displacement of an aperture ( 9 ) is carried out from its centered position in that one about a rotation axis ( 11 ) rotatable diaphragm disc ( 8th ), on the circumferentially several apertures ( 9 ) of different sizes, in relation to the optical axis ( 16 ) of the microscope illumination system ( 1 ) is arranged, that each aperture ( 9 ) by turning the aperture ( 8th ) in a starting position centered on the optical axis ( 16 ) and by further rotation within a predetermined range about the optical axis decentered to the optical axis ( 16 ) can be positioned. A method according to claim 21, characterized in that for the rotation of the diaphragm disc ( 8th ) a drive motor ( 10 ) is used, with the defined positions of the apertures ( 9 ) relative to the optical axis ( 16 ) are reproducibly adjustable. Method according to claim 21 or 22, characterized in that as light source ( 2 . 3 ) of the microscope illumination system ( 1 ) a light source ( 3 ) is used with a spectrum in the ultraviolet wavelength range. Method according to one of claims 21 to 23, characterized in that a light source ( 3 ) with a spectrum in the ultraviolet wavelength range and another light source ( 2 ) are used with a spectrum in the visual wavelength range, each via a dichroic beam splitter ( 4 ) in the beam path of the microscope illumination system ( 1 ) are coupled. Method according to one of claims 21 to 24, wherein the reference to the optical axis ( 16 ) centered or decentered illumination beam path ( 15 ) via a microscope objective ( 31 ) on the object to be examined ( 36 ), characterized in that, depending on the selected microscope objective ( 31 ) an associated aperture ( 9 ) in the starting position centered to the optical axis ( 16 ) is brought. Method according to one of claims 21 to 25, characterized in that with a camera ( 34 ) is generated to display a microscopic object image, a camera image, and that the camera image evaluated at least in terms of resolution and / or contrast and by rotation of the diaphragm disc ( 8th ) within the predetermined range around the optical axis ( 16 ) is optimized. Method according to one of claims 21 to 26, characterized in that with a camera ( 34 ) for displaying a microscopic object image, a camera image is generated, and that the camera image is evaluated at least in terms of resolution and / or contrast and by selecting an aperture ( 9 ) and / or a microscope objective ( 31 ) is optimized. Method according to one of claims 21 to 27, characterized in that with a camera ( 34 ) for displaying a microscopic object image, a camera image is generated, and that the camera image evaluated at least in terms of resolution and / or contrast and by selecting the light source ( 2 . 3 ) of the microscope illumination system ( 1 ) is optimized. Method according to one of claims 26 to 28, characterized in that the optimization of the camera image is at least in terms of resolution and / or contrast due to a selection of camera images and / or input of criteria by the user. Method according to one of claims 26 to 28, characterized in that the optimization of the camera image with respect to at least resolution and / or contrast is done automatically using an image analysis device. Method according to one of claims 21 to 30, characterized in that automatically or on the basis of a user input, a light source with a spectrum in the ultraviolet wavelength range for generating an illumination beam path ( 15 ' ) is activated and a predefinable or predetermined aperture ( 9 ) is reproducibly set to one or successively at a plurality of defined positions with respect to the optical axis. Method according to one of claims 26 to 30, characterized in that the optimization of the camera image takes place in that to various changeable settings on the microscope ( 30 ) and / or on the microscope illumination system ( 1 ) associated camera images of the same object area, to a selected section ( 51 ) within each camera image an intensity profile ( 52 ) and the generated intensity profiles ( 52 ) are evaluated and compared with regard to certain criteria, whereby the number of edges of an intensity profile ( 52 ) and / or the number of extreme values in an intensity profile ( 52 ) belong.

Images